/*
  三、基于下面提供的代码，完成后续的四个练习
 */

// 练习1：使用fp.add(x, y)和fp.map(f, x)创建一个能让functor里的值增加的函数ex1
const fp = require('lodash/fp')
const { Maybe, Container } = require('./support')
let maybe = Maybe.of([5, 6, 1])
let ex1 = num => maybe.map(fp.flowRight(fp.map(fp.add(num))))
console.log(ex1(2))

// 练习2：实现一个函数ex2，能够使用fp.first获取列表的第一个元素
let xs = Container.of(['do', 'ray', 'me', 'fa', 'so', 'la', 'ti', 'do'])
let ex2 = () => xs.map(fp.first)._value
console.log(ex2())

// 练习3：实现一个函数ex3，使用safeProp和fp.first找到user的名字的首字母
let safeProp = fp.curry(function(x, o) {
  return Maybe.of(o[x])
})
let user = { id: 2, name: 'Albert' }
let ex3 = () => safeProp('name', user).map(fp.first)._value
console.log(ex3())

// 练习4：使用Maybe重写ex4，不要有if语句
let ex4 = n => Maybe.of(n).map(parseInt)
console.log(ex4(null))
console.log(ex4(undefined))
console.log(ex4(''))